Identification of iron oxide phases in thin films grown on Al2O3(0 0 0 1) by Raman spectroscopy and X-ray diffraction

We report on the identification of Fe₃O₄ (magnetite) and α-Fe₂O₃ (hematite) in iron oxide thin films grown on α-Al₂O₃(0 0 0 1) by evaporation of Fe in an O₂-atmosphere with a thickness of a few unit cells. The phases were observed by Raman spectroscopy and confirmed by X-ray diffraction (XRD). Magnetite appeared independently from the substrate temperature and could not be completely removed by post-annealing in an oxygen atmosphere as observed by X-ray diffraction. In the temperature range between 400 °C and 500 °C the X-ray diffraction shows that predominantly hematite is formed, the Raman spectrum shows a mixture of magnetite and hematite. At both lower and higher substrate temperatures (300 °C and 600 °C) only magnetite was observed. After post-annealing in an O₂-atmosphere of 5 × 10^?5 mbar only hematite was detectable in the Raman spectrum.     

Internal Rotation of the Acetyl Methyl Group in Methyl Alkyl Ketones: The Microwave Spectrum of Octan-2-one

Methyl n-alkyl ketones form a class of molecules with interesting internal dynamics in the gas-phase. They contain two methyl groups undergoing internal rotations, the acetyl methyl group and the methyl group at the end of the alkyl chain. The torsional barrier of the acetyl methyl group is of special importance, since it allows for the discrimination of the conformational structures. As part of the series, the microwave spectrum of octan-2-one was recorded in the frequency range from 2 to 40 GHz, revealing two conformers, one with C₁ and one with C_s symmetry. The barriers to internal rotation of the acetyl methyl group were determined to be 233.340(28) cm⁻¹ and 185.3490(81) cm⁻¹, respectively, confirming the link between conformations and barrier heights already established for other methyl alkyl ketones. Extensive comparisons to molecules in the literature were carried out, and a small overview of general trends and rules concerning the acetyl methyl torsion is given. For the hexyl methyl group, the barrier height is 973.17(60) cm⁻¹ for the C₁ conformer and 979.62(69) cm⁻¹ for the C_s conformer.     

Site-specific immobilization of proteins at zeolite L crystals by nitroxide exchange reactions

Site-selective immobilization of dyes and different protein recognizing entities at the surface of zeolite L crystals using mild radical nitroxide exchange reactions is reported. Exposure of these crystals to aqueous protein solutions leads to site-selective immobilization of proteins onto the crystals.     

Adsorption and reduction of glutathione disulfide on α-Al2O3 nanoparticles: experiments and modeling

Glutathione disulfide (GSSG; γ-GluCysGly disulfide) was used as a physiologically relevant model molecule to investigate the fundamental adsorption mechanisms of polypeptides onto α-alumina nanoparticles. Its adsorption/desorption behavior was studied by enzymatic quantification of the bound GSSG combined with zeta potential measurements of the particles. The adsorption of GSSG to alumina nanoparticles was rapid, was prevented by alkaline pH, was reversed by increasing ionic strength, and followed a nearly ideal Langmuir isotherm with a standard Gibbs adsorption energy of -34.7 kJ/mol. Molecular dynamics simulations suggest that only one of the two glutathionyl moieties contained in GSSG binds stably to the nanoparticle surface. This was confirmed experimentally by the release of GSH from the bound GSSG upon reducing its disulfide bond with dithiothreitol. Our data indicate that electrostatic interactions via the carboxylate groups of one of the two glutathionyl moieties of GSSG are predominantly responsible for the binding of GSSG to the alumina surface. The results and conclusions presented here can provide a base for further experimental and modeling studies on the interactions of biomolecules with ceramic materials.     

Application of AC-SECM in corrosion science: local visualisation of inhibitor films on active metals for corrosion protection

The suitability of frequency-dependent alternating-current scanning electrochemical microscopy (4D AC-SECM) for investigation of thin passivating layers covering the surface of corrosion-inhibited metals has been demonstrated. Inhibition of copper corrosion by benzotriazole (BTAH) and methylbenzotriazole (MBTAH), which are effective inhibitors for this metal under many environmental conditions, was investigated. Strong dependencies were found for the AC z-approach curves with both the duration of the inhibitor treatment and the frequency of the AC excitation signal applied in AC-SECM. Both negative and positive feedback behaviours were observed in the AC approach curves for untreated copper and for Cu/BTAH and Cu/MBTAH samples. Negative feedback behaviour occurred in the low-frequency range, whereas a positive feedback effect was observed at higher frequencies. A threshold frequency related to the passage from negative to positive regimes could be determined in each case. The threshold frequency for inhibitor-modified samples was found always to be significantly higher than for the untreated metal, because the inhibitor film provides electrical insulation for the surface. Moreover, the threshold frequency increased with increasing surface coverage by the inhibitor. 4D AC-SECM was successfully applied to visualizing spatially resolved differences in local electrochemical activity between inhibitor-free and inhibitor-covered areas of the sample.     

Experimental and numerical investigations in skeletal muscle modelling

In the present paper, a method to compare displacement results of a muscle contraction simulation with results of optical experiments is proposed. A human skeletal muscle has been reconstructed to a volume element out of real two-dimensional MRI data. The surrounding tissue has also been taken into account in order to describe the interaction with other components in a realistic way. These regions of the interface have been supported by several spring stiffness. The numerical model has been fitted by this stiffness on one significant node. The results shown satisfied agreement with the optical experiments. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sensing the Molecular Structures of Hexan-2-one by Internal Rotation and Microwave Spectroscopy

Using two molecular jet Fourier transform spectrometers, the microwave spectrum of hexan-2-one, also called methyl n-butyl ketone, was recorded in the frequency range from 2 to 40 GHz. Three conformers were assigned and fine splittings caused by the internal rotations of the two terminal methyl groups were analyzed. For the acetyl methyl group CH₃ COC₃H₆CH₃, the torsional barrier is 186.9198(50) cm⁻¹, 233.5913(97) cm⁻¹, and 182.2481(25) cm⁻¹ for the three observed conformers, respectively. The value of this parameter could be linked to the structure of the individual conformer, which enabled us to create a rule for predicting the barrier height of the acetyl methyl torsion in ketones. The very small splittings arising from the internal rotation of the butyl methyl group CH₃COC₃H₆ CH₃ could be resolved as well, yielding the respective torsional barriers of 979.99(88) cm⁻¹, 1016.30(77) cm⁻¹, and 961.9(32) cm⁻¹.